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1-BMET5931 Nanomaterials in Medicine > L6 Magnetic NP > Flashcards

L6 Magnetic NP Flashcards

Re Quiz 5 W7

1
Q

Are iron oxide NPs biodegradable?

A

YES, IONPs biodegrade quite rapidly.

There is, however, released iron ions; the amount of iron ions released would be proportional to the amount of IONP administered, and one would have to assume that there’s a practical limit of IONP that can be safely administered

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2
Q

What does “large saturation magnetization” mean?

A

The “highest potential magnetic strength” of a material within a given external magnetic field (simplified terms).

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3
Q

Explain the following statement:

“In sufficiently small nanoparticles, magnetization can randomly flip directions under the influence of temperature”

(- Wikipedia)

A

NP need to be ‘single domain’ NP, which possess a single ‘magnetization direction/domain’. If the ambient temperature is high enough, and the particle is small enough, the magneitzation domain can randomly flip directions, resulting in a net zero magnetization in the absence of an external magnetic field, but non-zero magnetization in the presence of an external magnetic field; thus exhibiting superparamagnetism.

If ambient temperature isn’t high enough and the particle is too big (but still single-domain NP), then one can say there ‘isn’t enough energy’ to facilitate this random flipping, and the magnetization domain becomes ‘blocked’.

This temperature boundary would be called the ‘blocking temperature’ (defined as halfway bw ‘blocked’ and ‘superparamagnetic’, for a given NP size).

NB: Superparamagnetism is a stronger version of paramagnetism. Paramagnetism in essence describes the phenomenon where the material exhibits zero magnetism in the absence of an external magnetic field, but exhibits magnetism in the presence of an external magetic field. This is different to ferromagnetism, where the material retains its magnetic properties even without an external magnetic field, such as fridge magnets.

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4
Q

Explain the mechanisms of MRI

(per this lecture’s specifications)

A
  • MRI does not use ionizing radiation
  • MRI is based on the relaxation of proton spins in a magentic field
  • protons (hydrogen) are ‘excited’ by the external magnetic field
  • protons then ‘relax’ and emit radiofrequency, which is detected by the MRI
  • this relaxation profile is picked up by the MRI machine
  • the differences in the time-relaxation profile at a specified time is dependent on the tissue’s proton density, and is what generates the contrast between different tissues
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5
Q

In the context of IONPs, how might their visualisation for use in MRI be enhanced?

A

Although some tissues can be distinguished without contrast agents, most of the time, contrast agents are often needed to provide the difference of relaxation rates (since most tissues have similar proton density).

If you can get a specific tissue to ‘relax’ much faster than another though the use of MNP, then you will get better contrast.

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6
Q

Explain how IONPs may be used in Magnetic Hyperthermia

A

As a cancer treatment method, “the ferrofluid which contains iron oxide is injected to the tumor and then heated up by an alternating high frequency magnetic field. The temperature distribution produced by this heat generation may help to destroy cancerous cells inside the tumor.” (- Wikipedia)

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7
Q

Describe the main issue of MNPs that must be considered before their biomedical applications.

A

MNPs can stick together if they collide, which can lead to agglomeration due to attractive Van der Waals forces and magnetic dipolar interactions. This can be detrimental for applications.

To address this, organic surfactants may be utilised to preventing agglomeration. These are normally long-chain molecules, including fatty acids, dextran, alginate or other polymers.

(NB - avoid using the terms “agglomerate” and “aggregate” interchangeably; see https://onlinelibrary.wiley.com/doi/full/10.1002/jps.10191)

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8
Q
  1. List TWO biomedical applications of magnetic nanoparticles.

(2 marks)

A
  • MRI - imaging parts of the body (as contrast agents)
  • Magnetic hyperthermia (heat therapy) - you need a source of ‘Alternating Magnetic Field’ (AMF) → results in heating up of the magnetic nanoparticle (relying on heat to kill particular target cells, usually cancer cells)
  • Magnetic targeting and remote triggering thermal drug release
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9
Q
  1. List TWO characteristics of iron oxide nanoparticles (IONPs) that render them favourable for biomedical applications.

(2 marks)

A
  • Very stable, easy to synthesise, biocompatible, minimally toxic, biodegradable
  • Magnetic ← we can then use non-invasive techniques to control where the NP goes and to heat the NP up (needs to have reasonable large saturation magnetization)

(“Can be ‘activated’ into magnetic alignment in the body with an externally applied magnetic field”)

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10
Q
  1. Which of the following statements regarding iron nanoparticles and iron oxide nanoparticles is FALSE?

(A) Iron NPs are biocompatible

(B) Iron oxide NPs are biocompatible

(C) Magnetic properties of iron NPs (susceptible to further oxidation, whereas iron oxide are not) deteriorate due to oxidation in aqueous solution

(D) Magnetic properties of iron oxide NPs deteriorate due to oxidation in aqueous solution

A

(D) Magnetic properties of iron oxide NPs deteriorate due to oxidation in aqueous solution

  • (primarily the reason why iron oxide is more ‘popular’ in research than just pure iron NP)*
  • True:*

(C) Magnetic properties of iron NPs (susceptible to further oxidation, whereas iron oxide are not) deteriorate due to oxidation in aqueous solution

(A, B) Both Iron NPs and Iron oxide NPs are biocompatible

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11
Q
  1. Name ONE strategy to prevent agglomeration of magnetic NP in aqueous media.

(1 mark)

A

Surfactant coating

(there is only really this method) - polymeric coating, citrate, etc.

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12
Q
  1. Which of the following is NOT a valid statement about the function of the surfactant coating of magnetic nanoparticles?

(A) It can act as an anchor layer for functional groups

(B) It increases the magnetisation of the core

(C) It helps to prevents aggregation of magnetic nanoparticles

(D) It helps to provide colloidal stability

A

(B) It increases the magnetisation of the core.

Valid Statements:

(A) It can act as an anchor layer for functional groups (esp with certain polymeric coatings, these polymeric coatings can provide further functional groups for conjugation)

(C) It helps to prevents aggregation of magnetic nanoparticles

(D) It helps to provide colloidal stability.

(C and D are basically identical statements)

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13
Q
  1. Which of the following statements describes the relationship between single domain MNPs, multidomain MNPs, and their corresponding magnetic behaviour?

(A) Both single domain and multidomain MNPs are ferromagnetic

(B) Both single domain and multidomain MNPs are superparamagnetic

(C) Single domain MNPs are ferromagnetic; multi-domain MNPs are superparamagnetic

(D) Single domain MNPs are superparamagnetic; multi-domain MNPs are ferromagnetic

A

(D) Single domain MNPs are superparamagnetic; multi-domain MNPs are ferromagnetic

Incorrect:

(A) Both single domain and multidomain MNPs are ferromagnetic

(B) Both single domain and multidomain MNPs are superparamagnetic

(C) Single domain MNPs are ferromagnetic; multi-domain MNPs are superparamagnetic

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14
Q
  1. Which of the following statements is FALSE about superparamagnetic iron oxide NP (SPION)?

(A) SPIONs are single domain NPs.

(B) In the presence of an external magnetic field, SPION domains align and interact with the magnetic field.

(C) In the absence of an external magnetic field, SPION domains are randomly aligned and exhibit zero net magnetism.

(D) SPIONs maintain their randomly-aligned domains in the presence of an external magnetic field, thus exhibiting reduced agglomeration.

A

(D) SPIONs maintain their randomly-aligned domains in the presence of an external magnetic field (false, in the presence of external magnetic field, domains are aligned accordingly), thus exhibiting reduced agglomeration.

Less ‘magnetic-ness’ = less agglomeration
More ‘magnetic-ness’ = more agglomeration

True:

(A) SPIONs are single domain NPs. (by definition)

(B) In the presence of an external magnetic field, SPION domains align and interact with the magnetic field. (true, again, definition of superparamagnetism)​

(C) In the absence of an external magnetic field, SPION domains are randomly aligned and exhibit zero net magnetism. (true, same reasons as above) ​

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15
Q
  1. Iron oxide particle size synthesized through thermal decomposition can be controlled through solvent type.

TRUE or FALSE

A

TRUE

Different solvents leads to different IONP sizes

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16
Q
  1. Name ONE advantage of thermal decomposition method over coprecipitation method in the synthesis of iron oxide NP.
A
  • Easy and environmental-friendly production process
  • It can provide large scale synthesize
  • Relatively inexpensive
  • Better control of NP size/shape <
  • Better crystallinity hence better magnetic properties <
17
Q
  1. Which of the following best applies to the thermal decomposition technique of magnetic nanoparticle synthesis?

(A) Its use of organic solvents necessitates manipulation of the surface for transfer to aqueous media.

(B) No toxic chemicals are used.

(C) It provides poor monodispersity compared with other techniques.

(D) The high temperatures used lead to poor crystallinity of the magnetic nanoparticle, compared with other techniques.

A

(A) Its use of organic solvents necessitates manipulation of the surface for transfer to aqueous media.

  • These organic solvents provide a platform/medium to be able to work with dissolved precursors at high temperatures, usually higher than the boiling point of water (100ºC). But if you then just pour this NP into an aqueous solution without giving the NP particular coatings, the particles will aggregate.*
  • Regarding:*

(C) It provides poor monodispersity (single distribution of size/shape) compared with other techniques. (the con side of coprecipitation. Thermal decomposition provides better
monodispersity)

(D) The high temperatures used lead to poor crystallinity of the magnetic nanoparticle, compared with other techniques. (also the con side of coprecipitation. Thermal decomposition provides better crystallinity)​

18
Q
  1. Choose the correct statement:

A good contrast agent for MRI for either T1 or T2 would cause:

(A) A shorter/longer relaxation time at the tissue of interest, compared to the surrounding tissue.

(B) A similar relaxation time at the tissue of interest, compared to the surrounding tissue.

A

(A) A shorter/longer relaxation time at the tissue of interest, compared to the surrounding tissue.

The contrast is a function of the differences in the relaxation profile of the ‘proton response’ in the tissue/magnetic NP (different tissue will have different response)

19
Q
  1. True or False?

Contrast efficiency of iron oxide NP depends on their size.

A

TRUE

(they need to be small to be superparamagnetic though, so at least to that extent the size matters)

20
Q
  1. Name ONE characteristic/property for an ideal MRI contrast for imaging cells and biomolecules
A
  • High intracellular uptake and accumulation for cellular imaging
  • Facile delivery
  • Safe clearance
  • Minimal side effects
  • Superparamagnetism
21
Q
  1. List TWO advantages of MNP-based hypothermia treatment versus non-magnetic approaches, such as Au NP

(2 marks)

A
  • Can use external magnetic field to guide the MNP to target, (but Au can’t)
  • Biodegradable (better than Au)
  • Can be detected using MRI (Au can’t)
  • Can use RF (radiofrequency) to cross blood brain barrier (but Au can’t)

Note:

  • Combines diagnostics and therapeutics (so can Au)
  • MNP can circulate within the bloodstream (so can Au)
  • It can heat up the target tissue to the therapeutic level non-invasively (so can Au)
  • The above are advantages, but not necessarily over gold
  • Non-invasive (so can Au)
22
Q
  1. Which of the following parameters would determine the amount of heat energy dissipated by a specified amount of magnetic NP?

(There are 4 correct answers, you can only circle a maximum of 4 options, 0.5 mark each correct option)

(A) The type of magnetic material
(B) Size of NP
(C) Ambient temperature
(D) Shape of NP
(E) Strength of applied magnetic field
(F) The type of tissue where the NP resides in

A

(A) The type of magnetic material
(B) Size of NP
(C) Ambient temperature
(E) Strength of applied magnetic field

Incorrect:

(D) Shape of NP
(F) The type of tissue where the NP resides in

23
Q
  1. One example of magnetic iron nanoparticle-based drug delivery is a poly(N-isopropylacrylamide) (PNIPAM)-coated magnetic NP, with the drugs loaded within the PNIPAM-coating. Given that this PNIPAM coating ‘collapses’ at 40ºC and results in the subsequent release of the loaded drug, what would be the likely mechanism of controlled drug release for this particular NP system?

(A) The magnetic NP heats up upon interaction with certain biomarkers on a cancer cell, thus resulting in the collapse of the PNIPAM layer and subsequent release of drug.

(B) An external alternating magnetic field is applied once the magnetic NP is at its target location, subsequently heating up the magnetic NP, thus resulting in the collapse of the PNIPAM layer and subsequent release of drug.

(C) A cancer patient’s body temperature is ~40ºC, thus resulting in the collapse of the PNIPAM layer and subsequent release of drug upon intravenous injection.

(D) The interaction with the aqueous environment of the blood plasma causes the PNIPAM layer to collapse, thus resulting in the subsequent release of drug.

A

(B) An external alternating magnetic field is applied once the magnetic NP is at its target location, subsequently heating up the magnetic NP, thus resulting in the collapse of the PNIPAM layer and subsequent release of drug.

Heat → conformational change of the polymers that keep the drug trapped → controlled release of drug

1-BMET5931 Nanomaterials in Medicine (8 decks)

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